Traceback (most recent call last):
  File "/usr/bin/gtkdoc-mkhtml2", line 30, in <module>
    from gtkdoc import common, config, mkhtml2
  File "/usr/share/gtk-doc/python/gtkdoc/mkhtml2.py", line 106, in <module>
    from lxml import etree
ModuleNotFoundError: No module named 'lxml'